In general, for most business computers to operate satisfactorily, it is necessary for the computer to store, retrieve, and process data. The data utilized by the computer is stored in media elements. When the data stored in the media elements is to be processed, the data is retrieved from the media elements, and thereafter to be processed by processing circuitry of the computer.
On-line storage of the data in on-line media elements permits the processing circuitry of the computer to access the data in a nearly-instantaneous manner. However, on-line media element storage is relatively expensive.
Off-line storage of the data in off-line media elements requires greater amounts of time for the computer to access the data stored therein, but off-line media element storage is relatively inexpensive.
Because of the relatively low cost of off-Line media element storage, data generally not required to be accessed in a nearly-instantaneous manner is usually stored in off-line media element storage. Data which is duplicative of data stored in on-line media elements is another example of data which is usually stored in off-line media elements.
Data is sometimes referred to as being "archived" when the data is stored in the off-line media elements. Archiving of data in the off-line media elements provides a relatively inexpensive means by which the data may be stored for extended time periods. Examples of off-line media elements which are oftentimes utilized to archive data include magnetic tapes (such as magnetic tapes housed within cartridges and referred to as media cartridges), magnetic discs, head disc assemblies, and optical discs. Media elements typically utilized to archive media are also, at times, referred to as archival-type media elements.
In many instances, large amounts of data are archived, thereby necessitating large numbers of off-line media elements to be utilized to store the data. The media elements are typically catalogued and stored in indexed, storage locations to facilitate subsequent retrieval of selected ones of the media elements.
Automated storage and retrieval apparatus is available to facilitate retrieval of the off-line media elements and permit a computer to access the data stored thereon. Such equipment typically includes fixed-location storage bins in which the media elements are stored. The storage bins are shelf-like assemblies in which the shelves of the storage bins define bin locations and the media elements are stored in the bin locations of the storage bins. A plurality of fixed-location storage bins are positioned in many different arrangements.
The automated storage and retrieval apparatus also includes a media element handler, or transport, mechanism. The media element handler mechanism is a remotely-controlled device which is capable of articulate movement to retrieve media elements stored in bin locations of the fixed-location storage bins.
When data stored on a selected media element positioned in a particular bin location of a storage bin is to be retrieved, appropriate commands are given to the media element handler mechanism to retrieve the selected media element. The media element handler mechanism includes actuator positioners which locate the handler mechanism in, for example, the X and Y directions and to orient the handler mechanism relative to the storage bins; and the bin locations thereof.
When the handler mechanism locates the bin location of the storage bin in which the selected media element is positioned, grasping arms of the handler mechanism grasp the selected media element, remove the media element from the bin location of the storage bin, and provide the selected media element to a media drive, such as a magnetic tape reader, an optical disc drive, a magnetic disc drive, or a receptacle for a head disc assembly. The media drive allows the data stored in the media element to be accessed by the processing circuitry of the computer. Data may also be stored on the media element by the computer by way of the media drive.
When the computer is required to access data stored on more than one media element, the media elements on which the data is stored are retrieved in a serial manner. That is to say, the media element handler mechanism of existing media retrieval equipment first retrieves a first media element and provides the first media element to the media drive whereat the data stored on the first media element is accessed by the computer. Thereafter, the handler mechanism returns the first media element to the bin location of the storage bin. The media handler then retrieves a second media element, and the same sequence is repeated with the second media element. Additional media elements are retrieved in similar fashion.
As the steps required to retrieve each media element must be performed serially, retrieval of each additional media element requires a cumulative increase in the amount of time required of the existing equipment to complete retrieval operations. When large numbers of media elements must be retrieved by the retrieval equipment, the amount of time required to retrieve all of such media elements to permit access by the computer to the data stored thereon can become significant.
Also, a large number of media elements are typically stored in bin locations of a large number of storage bins. Because the media element handler mechanism must retrieve a media element located in a bin location of any of the fixed-location storage bins, the handler mechanism must be capable of movement to any of the storage bins to retrieve media elements stored therein. Therefore, the handler mechanism must be capable of relatively complex movements, and, accordingly, is typically a relatively costly device.
It is with respect to these considerations and other background information relative to automated storage and retrieval equipment that the significant improvements of the present invention have evolved.